1. Field of the Invention
The present invention relates to steering angle sensors and, more particularly, absolute steering angle sensors.
2. Description of the Related Art
A wide variety of steering angle sensors are known in the art for providing steering angle data to vehicle systems such as vehicle stabilizing systems. Such steering angle sensors may be broadly classified as either absolute position sensors or relative position sensors.
Relative position steering angle sensors register an initial zero position when the ignition is turned on and output data that defines the change in the steering angle relative to the initial “zero” position of the steering wheel. To determine the actual steering angle position of the vehicle with such a relative position steering angle sensor, the offset between the initial steering wheel position and the “true” zero steering angle must be determined. The offset may be determined by the vehicle controller using vehicle model equations and data obtained from other vehicle sensors such as a yaw sensor and individual wheel speed sensors. This determination of the offset value may place a relatively significant computational burden on the vehicle controller.
In contrast, absolute position steering angle sensors output the actual or “true” steering angle, rather than the relative difference between the current steering angle and the initial steering wheel position when the ignition was turned on. Generally, absolute steering angle sensors place fewer computational demands on the controller but are more expensive than relative position steering angle sensors.
The steering range of a motor vehicle typically extends between four and five complete 360 degree revolutions between the left and right steering lock positions of the steering wheel. For example, the steering range may extend 1500°, i.e., four complete revolutions plus 60°. Measuring absolute steering angle over the entire steering range is typically a more complex task than providing either the absolute steering angle within just one revolution of the steering wheel or the relative steering angle, which provides no absolute measurement with respect to the true position of the steering wheel.
What is needed in the art is a cost effective device for providing an accurate measurement of absolute steering angle over the entire steering range of a vehicle.